Field
This disclosure relates generally to expiratory limbs for use in respiratory circuits, and in particular to a breathing circuit with an improved drying expiratory limb configured to provide improved drying performance by providing a tailored temperature profile along the tube.
Description of Related Art
In medical applications, various components transport gases having high levels of relative humidity to and from patients. Condensation, or “rain out,” can be a problem when the high humidity gases come into contact with the walls of a component at a lower temperature. However, condensation is dependent on many factors, including not only the temperature profile in the component, but also the gas flow rate, component geometry, and the intrinsic “breathability” of the material used to form the component, that is the ability of the material to transmit water vapor, while substantially resisting the bulk flow of liquid water and the bulk flow of gas.
For example, PAP systems (ventilation systems that provide patients with breathing gases at positive pressure) use breathing tubes for delivering and removing inspiratory and expiratory gases. In these applications, and in other breathing applications such as assisted breathing, the gases inhaled by a patient are usually delivered through an inspiratory limb at humidity near saturation. The breathing gases exhaled by a patient flow through an expiratory limb and are usually fully saturated. Condensation may form on the interior walls of a breathing circuit component during patient inhalation, and significant condensation levels may form during patient exhalation. In addition, condensation may occur where the exhaled gases enter the ventilator. Such condensation is particularly deleterious when it is in close proximity to the patient. For instance, mobile condensate forming in a breathing limb (either inspiratory or expiratory) can be breathed or inhaled by a patient and may lead to coughing fits or other discomfort.
Many gas humidification systems deliver heated and humidified gases for various medical procedures, including respiratory treatment, laparoscopy, and the like. These systems can be configured to control temperature, humidity and flow rates through the use of sensors. To reduce or avoid condensation or rain out, a breathing circuit can have heaters associated with gas conduits where the heaters provide heat to the gas as it flows to and/or from the user. The conduit heaters can be controlled to provide heat to the gas so that the gas maintains a suitable temperature and/or humidity.